Vibration and stability of a primary seal ring is controlled by a secondary seal system. An inflatable bladder which forms a portion of the secondary seal varies the damping applied to this seal ring. The amplitude of vibration of the primary seal ring is sensed with a proximity probe that is connected to a microprocessor in a control system. The bladder pressure is changed by the control system to mitigate any sensed instability or vibration

Dirusso, E.

English

NASA Technical Reports Server

United States Patent [191 
DiRusso 
[I  11 Patent Number: 4,580,791 
[45] Date of Patent: Apr. 8, 1986 
[54] VARIABLE FRICTION SECONDARY SEAL 
[75] Inventor: Eliseo DiRusso, Westlake, Ohio 
[73] Assignee: The United States of America as 
represented by the Administrator, 
National Aeronautics and Space 
Administration, Washington, D.C. 
FOR FACE SEALS 
[21] Appl. No.: 672,224 
[22] Filed: Nov. 16,1984 
[51] Int. Cl.4 ............................................... F16J 15/34 
[58] Field of Search ....................... 277/3, 27, 28, 96.1 
[561 References Cited 
[52] U.S. Cl. .: ....................................... 277/27; 277/28 
U.S. PATENT DOCUMENTS 
3,330,563 7/1967 DePuydt et al. ..................... 277/29 
4,103,903 8/1978 Capriotti et al. ...................... 277/27 
4,193,756 3/1978 Leon ....................................... 432/3 
4,351,574 9/1982 Furukawa et al. ................. 308/3 A 
4,408,767 10/1983 Kako ..................................... 277/27 
4,447,063 5/1984 Kotzur et al. ......................... 277/28 
4,471,964 9/1984 Kotzur .................................. 277/27 
4,483,541 11/1984 DeVenyi et al. ..................... 277/27 
4,529,209 7/1985 Nii ...................................... 277/96.1 
FOREIGN PATENT DOCUMENTS 
645359 7/1962 Canada .................................. 277/28 
Primary Examiner-Robert I. Smith 
Attorney, Agent, or Firm-Gene E. Shook; John R. 
Manning 
1571 ABSTRACT 
Vibration and stability of a primary seal ring 18 is con- 
trolled by a secondary seal system 24. An inflatable 
bladder 26 which forms a portion of secondary seal 
varies the damping applied to this seal ring. 
The amplitude of vibration of the primary seal ring 18 is 
sensed with a proximity probe 34 that is connected to a 
microprocessor in a control system 32. The bladder 
pressure is changed by the control system 32 to mitigate 
any sensed instability or vibration. 
14 Claims, 1 Drawing Figure 
32 
https://ntrs.nasa.gov/search.jsp?R=19860016318 2020-03-23T07:05:10+00:00Z
U.S. Patent Apr. 8,1986 4,580,79 1 
1 
VARIABLE FRICTION SECONDARY SEAL FOR 
FACE SEALS 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the government for 
governmental purposes without the payment of any 
royalties thereon or therefor. 
TECHNICAL FIELD 
This invention is concerned with improving self act- 
ing radial face seals of the type which operate with a 
very thin liquid or gaseous film between the primary 
seal faces. Face seals in general and particularly “self- 
acting” face seals are subject to instability caused by the 
vibration of the primary seal ring which may lead to 
excessive seal face wear or failure. 
Face-type fluid seals are shaft seals generally com- 
prising a nonrotating or stationary seal face and a rotor 
ring provided to rotate with the shaft and having a face 
opposing that of the stator seal, the opposing faces ex- 
tending radially outwardly from the periphery of the 
shaft, thereby effecting a seal between the low-pressure 
and high-pressure regions of a surrounding and engulf- 
ing fluid. Radial face seals operate with extremely small 
gaps between the stationary or primary seal ring and the 
opposing face of the rotor ring or seal seat. 
It is necessary that the tolerances for the existing 
space or gap be closely monitored so that the existing 
gap is held as closely as possible to its design value so as 
to avoid excessive fluid leakage or high friction loss. To 
realize this, the primary seal ring must be placed in a 
stabilized condition both under hydrostatic as well as 
hydrodynamic conditions. That is, proper equilibrium 
must be reached between high-pressure and low-pres- 
sure regions both under conditions when the liquids 
involved are at rest and to the pressures they exert or 
transmit as well as under conditions when motion of the 
fluids exert a force which acts on the elements of the 
seal immersed in the fluids. 
Conventional radial face seals consisting of a primary 
seal ring or stator member and a rotor seal ring are 
inherently unstable. This instability is generally due to 
an angular misalignment brought about by a hydrody- 
namic effect establishing a pressure differential that 
produces a transverse moment which alters and disturbs 
the seal of the primary or stator seal ring. This pressure 
distribution produces dynamic instability that has a 
deterimental effect upon the resulting seal. 
Prior art devices usually left the damping of primary 
seal ring vibrations to chance. When it was addressed, 
the damping was set to satisfy a given seal operating 
condition and could not be varied to accommodate 
different seal operating conditions or transient condi- 
tions. The disadvantage of such devices was that the 
seal vibrations were acceptable for only one design 
condition, and instabilities were encountered when seal 
conditions deviated from the design condition or when 
the seal was perturbed by transients. 
In addition to the primary sealing face, all face seals 
have a secondary seal, typically in the form of piston 
rings or elastomeric “0” rings. The secondary seal 
functions to seal the secondary leak path in the face seal 
assembly. 
4,5 80,79 1 
BACKGROUND ART 
U.S. Pat. No. 3,330,563 to De Puyt et a1 is directed to 
an inflatable seal structure where the seal is particularly 
5 useful in preventing the entry of water and dirt into 
bearing assemblies on boat trailer wheels. 
U.S. Pat. No. 4,103,903 to Capriotti et a1 is concerned 
with a fluid accuated sealing arrangement. An accuat- 
ing fluid is utilized for both biasing a rotatable sealing 
lo element into sealing association with a portion of a 
rotatable member and for providing the necessary lubri- 
cation of the rotatable sealing element. 
U.S. Pat. No. 4,193,756 to Leon relates to a seal for a 
15 rotating apparatus, such as a rotary kiln. Pressurized 
bellows are employed to bias the seal. 
U.S. Pat. No. 4,351,574 to Furukawa et al describes a 
load compensated type guide mechanism. A pressurized 
fluid is employed in response to a change in perpendicu- 
2o lar displacement of a machine part with respect to a 
guide surface. 
DISCLOSURE OF THE INVENTION 
It is, therefor, an object of the present invention to 
25 provide apparatus for controlling the vibration and 
stability of a primary seal ring. Another object is to 
provide a secondary seal system which can vary the 
friction force or damping applied to the primary seal 
ring thereby controlling its vibration and stability. 
According to the present invention an inflatable biad- 
der forms not only a part of a secondary seal, but also 
the means to adjust the tightness of the secondary seal. 
An appropriate feedback mechanism is used to pump 
adequate amounts of fluid into this bladder. 
The face seal’s stability can be controlled as a func- 
tion of primary ring vibration amplitudes. Also the 
friction can be remotely changed to achieve acceptable 
vibration amplitudes for a large range of seal operating 
conditions without compromising the secondary seal 
BRIEF DESCRIPTION OF THE DRAWING 
The objects, advantages and novel features of the 
invention will be more fully apparent from the follow- 
45 ing detailed description when read in connection with 
the accompanying drawing which is an axial quarter 
section of a variable friction secondary seal constructed 
in accordance with the invention. 
BEST MODE FOR CARRYING OUT THE 
INVENTION 
Referring now to the drawing, there is shown a shaft 
10 which rotates about its normal axis Y-Y’. The shaft 
55 10 extends into a container 12 enclosing a body of fluid 
14. The pressure of the fluid 14 is higher than the pres- 
sure outside the container 12. Loss of fluid 14 from the 
container 12 is prevented by a sealing apparatus of the 
face sealed type. The operation of such apparatus is 
60 discussed in U.S. Pat. Nos. 3,675,935, 4,260,166 and 
4,291,877. 
The face seal incorporates a rotatable seat 16 in the 
form of a shoulder mounted on the shaft 10. The seal 
further includes a primary seal ring in the form of an 
65 annular plate 18 through which the shaft 10 extends. 
The annular plate 18 is rigidly secured to a tubular 
carrier 20 in the form of a nose piece which is recipro- 
cally mounted in the container 12. 
3 0  
35 
40 performance. 
50 
4,580,791 
A spring 22 biases the carrier 20 and annular plate 18 
toward the rotatable seat 16. Rotation of the carrier 20 
is prevented by conventional anti-rotation means. 
A dam formed by the sealing engagement of the sur- 
faces of the seat 16 and the annular plate 18 prevents 
leakage of the fluid 14. This engagement of the seat 16 
and the annular plate 18 forms a face seal, and the sur- 
faces are preferably optically flat. 
During rotation of the shaft 10 the seal seat 16 and 
annular plate 18 are separated by a thin fluid film in a 
manner well known in the art. This is shown in the 
drawing. 
The fluid film may encounter conditions in which it is 
unstable. For example, the annular plate 18 may vibrate 
through large amplitudes of fluid film thickness. This 
vibration causes intermittant contact of the seal seat 16 
and the annular plate 18 which results in excessive seal 
wear and deteriorated performance. 
According to the present invention a variable friction 
secondary seal 24 is incorporated into the sealing appa- 
ratus. This secondary seal 24 not only seals the leak path 
between the carrier 20 and the container 12, but also 
controls the stability of the primary seal ring in the 
event these vibrations become excessive. 
This variable friction secondary seal 24 comprises an 
inflatable bladder 26 which engages a sealing member in 
the form of a secondary seal ring 28 that is mounted in 
the container 12. The secondary seal ring 28 has a tubu- 
lar configuration and extends around the carrier 20. 
An axial split line in the ring 28 enables the diameter 
of the ring to be selectively varied through a small 
predetermined range. The secondary seal ring 28 is 
maintained in sealing engagement with the carrier 20 by 
expansion of the bladder 26. 
During rotation of the shaft 10 variable friction and, 
consequently, variable damping are achieved by selec- 
tively introducing variable amounts of air or the hy- 
draulic pressure through a stem 30 extending from the 
bladder 26. This causes the bladder 26 to expand or 
contract thereby varying th,e pressure in the secondary 
seal ring 28. Such action alters the radial force and, 
consequently, the friction damping applied to the car- 
rier 20. 
In the event the seal film becomes unstable or the 
primary ring 18 begins to vibrate, the bladder pressure 
is changed to mitigate the instability or vibration. The 
bladder pressure is preferably changed by a feedback 
control system 32 which utilizes a microprocessor. The 
vibration amplitude of the primary seal ring is sensed by 
a proximity probe 34 mounted in the annular plate 18 
and connected to the microprocessor through a lead 36. 
The control system 32 then changes the bladder pres- 
sure to minimize or limit the primary ring vibration 
amplitudes to be within stable boundries. It is contem- 
plated that the bladder pressure may be changed manu- 
ally through a suitable valve means. 
The secondary seal material may be selected to pro- 
vide many different friction coefficients. Also coatings 
may be applied to the secondary seal ring to optimize 
the friction coefficient and sliding interface. 
While the preferred embodiment of the invention has 
been shown and described it will be obvious that certain 
structural modifications may be made without depart- 
ing from the spirit of the invention or the scope the 
subjoined claims. 
I claim: 
1. In apparatus for sealing a rotatable shaft extending 
into a container of fluid of the type having a seat mem- 
5 
10 
15 
20 
25 
30 
35 
40 
45 
5 0  
55  
60 
65 
4 
ber mounted on said shaft for rotation therewith and an 
annular member mounted on a tubular carrier member 
extending around said shaft in spaced relationship 
thereto and mounted on said container for a reciprocat- 
ing movement toward and away from said seat along 
the axis of rotation of said shaft with means for biasing 
said annular member into engagement with said seat 
thereby forming a primary seal, the improvement com- 
prising 
a secondary seal in said container in frictional engage- 
ment with said carrier member to accomodate the 
reciprocating movement thereof while preventing 
leakage of the fluid therebetween, and 
means for selectively varying the friction between 
said secondary seal and said carrier thereby con- 
trolling the stability of said primary seal. 
2. Apparatus as claimed in claim 1 wherein 
said secondary seal comprises a ring member in en- 
gagement with said carrier member and an inflat- 
able bladder in engagement with said ring and said 
container, and 
said friction varying means includes a control device 
for selectively varying the pressure within said 
bladder. 
3. Apparatus as claimed in claim 2 wherein said ring 
member has an annular configuration for extending 
around said carrier member and an axial split line to 
enable the diameter thereof to be varied. 
4. Apparatus as claimed in claim 2 including means 
for sensing instability of the primary seal and control- 
ling the pressure within said bladder in response 
thereto. 
5. In combination with a radial face seal of the type 
wherein a seat on a rotating shaft is separated from a 
non-rotating annular member on a carrier reciprocably 
mounted in a container by a film of fluid enclosed by 
said container, the improvement comprising 
means for selectively limiting the amplitudes of vibra- 
tions of said annular member when said seal film 
becomes unstable. 
6. Apparatus as claimed in claim 5 wherein the vibra- 
a secondary seal mounted in the container for fric- 
tional engagement with said carrier to accomodate 
reciprocable motion, and 
means for selectively varying the friction of said sec- 
ondary seal. 
7. Apparatus as claimed in claim 6 wherein 
the secondary seal comprises a metal member for 
engaging said carrier and an inflatable bladder in 
engagement with said metal member and said con- 
tainer. 
8. Apparatus as claimed in claim 7 wherein said metal 
member has an annular configuration and an axial split 
line to enable the diameter thereof to be varied. 
9. Apparatus as claimed in claim 7 including means 
for controlling the pressure within said bladder in re- 
sponse to instability of said seal film. 
10. Apparatus as claimed in claim 9 including a prox- 
imity probe for sensing the instability of said seal film. 
11. Apparatus as claimed in claim 10 wherein the 
proximity probe is mounted in said ring member. 
12. A secondary seal for use in combination with a 
primary seal of the type having a seat and an annular 
plate on a carrier member mounted on a container for 
reciprocating movement toward and away from said 
seat, said secondary seal comprising, 
tion amplitude limiting means comprises 
4,5 80,79 1 
5 6 
a sealing member in engagement with said carrier 
member, 
an inflatable bladder in engagement with said sealing 
member and said container, and 
means for selectively controlling the pressure within 5 
said bladder thereby varying the friction between 
the carrier member and the container. 
13. A secondary seal as claimed in claim 12 including 
means for sensing instability of the primary seal and 
controlling the pressure within said bladder in response 
thereto. 
14. A secondary seal as claimed in claim 13 including 
a proximity probe for sensing instability of said primary 
seal. 
* * * * *  
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 


Variable friction secondary seal for face seals

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server